1. Field of the Invention
The present invention relates to a pneumatic tire with excellent properties which have not been attained in the conventional tires, wherein 4,6-nylon is used in carcass cords in the case of pneumatic radial tires in which cords of belt layer may be steel, aramide, PET (polyester) or composite thereof or in breaker or carcass cords in the case of pneumatic bias tires.
2. Related Art Statement
As the material for the carcass cords in the conventional radial tires, use have been made of steel, aramide, nylon, PET, rayon and so on. In the tires having a relatively high internal pressure with a heavy load, steel, aramide, and PET are used. Meanwhile, nylon, PET, rayon and the like are used in the passenger car ties having a relatively low internal pressure. This reason is that it is preferable that under the high internal pressure and heavy load, the elongation of the material of the carcass cords is made small (modulus being high) and the strain of the belt edges or the carcass edges of the radial tires is made as small as possible, and that the modulus is rather lower in the case of the passenger car tires because the riding comfortably is made much of. However, the material of the carcass cords suitably used in the medium range has been recently desired in that the internal pressure is made higher to lower the rolling resistance and the radial tires have become popularized for the light trucks. Although PET and nylon are ordinarily used as general purpose materials in this range, PET undergoes hydrolysis with amine component in the rubber, and therefore countermeasure is required to make heat generation of the tire as small as possible. On the other hand, nylon has a small modulus and a large elongation under application of the internal pressure and load. Thus, nylon remains unsatisfactory for the durability.
Next, with respect to the required characteristics as the cord material of the carcass in the bias tires, the cord material having excellent flex fatigue performance relative to the repeated strain of the tire is preferentially used, and the nylon is now mainly used. However, to the contrary, there have been strongly demanded improvement on the cornering stability and reduction in noise level as the required performances of the recent bias tires, which are coped with by replacing the nylon by PET. However, as to PET, there is a deterioration problem due to hydrolysis in the rubber as mentioned above, and it is an actual situation that PET can be used only up to tires having a small heat generating property.